Closes #1941

This change normalized accent characters when searching dandisets. For example (from that issue), the words Buzsaki and Buzsáki would now resolve to the same word in search.

It seems the introduction of this change has no real impact on the query performance. In fact, perhaps due to now using a less complex search function overall (since we're no longer using the DRF SearchFilter class), the performance seems to be ever so slightly better.

Postgres docs for the unaccent extension: https://www.postgresql.org/docs/current/unaccent.html
Django docs for unaccent: https://docs.djangoproject.com/en/5.1/ref/contrib/postgres/lookups/#unaccent

Of note, we can't simply use the __unaccent__ lookup without any other changes, as is shown in the Django docs, because the metadata field is a JSONField, and that lookup only works on Charfield and Textfield.